1. Field of the Invention
The present invention relates to a novel liquid crystalline compound and a liquid crystal composition (hereinafter referred to merely as a composition according to circumstances). More specifically, it relates to a liquid crystalline compound having a SiH3 group at an end, a composition comprising the same and a liquid crystal display constituted using this composition. The term xe2x80x9cliquid crystalline compoundxe2x80x9d used in the present invention is a general term for a compound showing a liquid crystal phase and a compound which does not show a liquid crystal phase but is useful as a component for a liquid crystal composition.
2. Description of the Related Art
A liquid crystal display (LCD) making use of characteristics of a nematic liquid crystal phase is widely used for various uses including monitors for personal computers and portable telephones, and demand therefor has been growing large year by year. In accordance with it, improvement items for performances required for LCD have come to extend over many divergences such as an expansion in an operable temperature range, a shift to a high density and coloring of a display picture plane, an acceleration in response and an expansion in a viewing angle. Various display modes using electro-optical effects, such as a DS (Dynamic Scattering) mode, a TN (Twisted Nematic) mode, a GH (Guest Host) mode, an STN (Super Twisted Nematic) mode, an IPS (In-Plane switching) mode, a VA (Vertical Alignment) mode and OCB (Optically Compensated Bend) have been proposed in order as means for solving them.
In such situation, various characteristics are required to a composition used for LCD according to the respective display modes. First, the physical property values such as a birefringence (xcex94n), a dielectric anisotropy (xcex94∈), a viscosity (xcex7), a conductivity and an elastic constant ratio K33/K11 (K33: bend elastic constant and K11: spray elastic constant) of a liquid crystal composition are required to have values which are optimum for a display mode and a form of an element. Further, in order to achieve high-speed response in any of the LCD""s shown above, a composition having a low viscosity is required, and a liquid crystalline compound has to be indispensably reduced as well in a viscosity. In addition thereto, given as common items of characteristics required to a composition are stability against moisture, light, heat and air which are usually present under an use environment and stability against an electric field and electromagnetic irradiation. Further, it is important that a liquid crystalline compound constituting a composition is chemically stable under use conditions and that they have a good solubility with each other.
In the existing state, however, it is very difficult to solve these problems only with the existing liquid crystal compounds and compositions, and it is an urgent matter to develop a novel liquid crystalline compound and composition which can meet the various requirements described above.
In recent years, development of various techniques in a liquid crystal display has been tried for the purpose of an enlargement in a picture plane. Especially, liquid crystal compositions which contribute largely to a reduction in power consumption and high speed response are desired to be developed. It is essential for a reduction in power consumption to further reduce a threshold voltage of a composition (E. Jakeman et al., Phys. Lett., 39A. 69 (1972)). Also, a low viscosity is important as well for high speed response. Various compounds have so far been developed in order to achieve these objects. For example, compounds having a silyl group in a molecule represented by the following formulas (a), (b) and (c) are known respectively according to Japanese Patent Application Laid-Open No. 9653/1994, Japanese Patent Application Laid-Open No. 2878/1995 and Japanese Patent Application Laid-Open No. 2879/1995: 
In these compounds, silicon is substituted with three alkyl groups. For example, the present inventors measured the physical property values of a compound having a propyldimethylsilyl group represented by the following formula (d) to find the problem that it had not only a markedly high viscosity but also an unsatisfactory mutual solubility with other components constituting a composition: 
Physical property measurement: a nematic phase-isotropic phase transition temperature (NI) and a viscosity (xcex7) at 20xc2x0 C. of a liquid crystal composition ZLI-1132 manufactured by Merck Co., Ltd. were 72.6xc2x0 C. and 26.7 mPaxc2x7s respectively. Then, 15% by weight of the compound represented by the formula (d) was added to 85% by weight of this composition, and NI and xcex7 of the resulting composition were determined to find that they were 15xc2x0 C. or lower and 39.7 mPaxc2x7s respectively. It has been found from this result that a composition prepared using the compound represented by the formula (d) is not only notably increased in a viscosity but also reduced in NI by 50xc2x0 C. or lower. Further, the compound represented by the formula (d) was inferior in mutual solubility with the other compositions.
An object of the present invention is to solve problems on conventional techniques and provide a novel silicon compound which has a low viscosity and a low threshold voltage and which is improved in mutual solubility, a composition comprising the same and a liquid crystal display using the above composition.
In order to achieve the objects described above, the following inventions are claimed for the grant of a patent in the present application.
[1] A silicon compound represented by formula (1): 
wherein Y1 is alkylene having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in this alkylene may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 and xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94 and xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94 and SiH3, or xe2x80x94Sxe2x80x94 and SiH3 are not adjacent, and at least one hydrogen in the alkylene may be replaced by halogen or xe2x80x94CN; Y2 is hydrogen, halogen, xe2x80x94CN, xe2x80x94Cxe2x89xa1Cxe2x80x94CN, or alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, or xe2x80x94Cxe2x89xa1Cxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 and xe2x80x94Sxe2x80x94, or xe2x80x94Oxe2x80x94 and xe2x80x94Sxe2x80x94 are not adjacent, and any hydrogen in the alkyl may be replaced by halogen or xe2x80x94CN; A1, A2, A3, and A4 each are independently 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene, or 1,4-phenylene in which any hydrogen is replaced by halogen; in which any hydrogen in 1,4-cyclohexylene or 1,4-cyclohexenylene may be replaced by halogen, any xe2x80x94CH2xe2x80x94 in these rings may be replaced by xe2x80x94Oxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and any xe2x80x94CHxe2x95x90 in 1,4-phenylene may be replaced by xe2x80x94Nxe2x95x90; Z1, Z2 and Z3 each are independently a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94(CH2)3Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCF2xe2x80x94, or xe2x80x94CF2Oxe2x80x94; and p and q each are independently 0 or 1.
[2] The silicon compound defined in the above item [1], wherein in formula (1) described above, p and q are 0; A1 and A2 each are independently 1,4-cyclohexylene, 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene, 1,4-phenylene in which any hydrogen is replaced by halogen, or pirimidine-2,5-diyl; and Z1 is a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CH=CHxe2x80x94, xe2x80x94C=Cxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCF2xe2x80x94, or xe2x80x94CF2Oxe2x80x94.
[3] The silicon compound defined in the above item [1], wherein in formula (1) described above, p is 1, and q is 0; A1, A2 and A3 each are independently 1,4-cyclohexylene, 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene, 1,4-phenylene in which any hydrogen is replaced by halogen, or pirimidine-2,5-diyl; and Z1 and Z2 each are independently a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94OCF2xe2x80x94, or xe2x80x94CF2Oxe2x80x94.
[4] The silicon compound defined in the above item [1], wherein in formula (1) described above, p and q are 1; A1, A2, A3, and A4 each are independently 1,4-cyclohexylene, 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene, 1,4-phenylene in which any hydrogen is replaced by halogen, or pirimidine-2,5-diyl; and Z1, Z2 and Z3 each are independently a single bond, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94OCF2xe2x80x94, or xe2x80x94CF2Oxe2x80x94.
[5] The silicon compound defined in the above item [1], wherein in formula (1) described above, Y1 is alkylene having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in this alkylene may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 or xe2x80x94Oxe2x80x94 and SiH3 are not adjacent; Y2 is alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent; and A1, A2, A3, and A4 each are independently 1,4-cyclohexylene, 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene, or pirimidine-2,5-diyl.
[6] The silicon compound defined in the above item [1], wherein in formula (1) described above, Y1 is alkylene having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkylene may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 or xe2x80x94Oxe2x80x94 and SiH3 are not adjacent; Y2 is halogen, xe2x80x94CN, xe2x80x94Cxe2x89xa1Cxe2x80x94CN or alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and at least one hydrogen is replaced by halogen; and A1, A2, A3, and A4 each are independently 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene, 1,4-phenylene in which at least one hydrogen is replaced by halogen, or pirimidine-2,5-diyl.
[7] The silicon compound defined in the above item [1], wherein in formula (1) described above, Y1 is alkylene having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkylene may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 or xe2x80x94Oxe2x80x94 and SiH3 are not adjacent; Y2 is alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 and xe2x80x94Sxe2x80x94, or xe2x80x94Oxe2x80x94 and xe2x80x94Sxe2x80x94 are not adjacent; A1, A2, A3, and A4 each are independently 1,4-cyclohexylene, 1,4-cyclohexylene in which one or more non-adjacent xe2x80x94CH2xe2x80x94 are replaced by xe2x80x94Oxe2x80x94, 1,4-phenylene in which a 2-position is replaced by halogen, 1,4-phenylene in which a 3-position is replaced by halogen, or 1,4-phenylene in which a 2-position and a 3-position are replaced by halogen, and one of A1, A2, A3, and A4 is always 1,4-phenylene in which a 2-position or a 3-position is replaced by halogen or 1,4-phenylene in which a 2-position and a 3-position are replaced by halogen.
[8] A liquid crystal composition comprising at least one silicon compound defined in any one of the items [1] to [7].
[9] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any one of the items [1] to [7] as a first component and at least one compound selected from the group of compounds represented by formulas (2), (3) and (4) as a second component: 
wherein R1 is alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and any hydrogen in the group may be replaced by fluorine; X1 is fluorine, Chlorine, xe2x80x94OCF3, xe2x80x94OCF2H, xe2x80x94CF3, xe2x80x94CF2H, xe2x80x94CFH2, xe2x80x94OCF2CF2H, or xe2x80x94OCF2CFHCF3; L1 and L2 each are independently hydrogen or fluorine; Z4 and Z5 each are independently xe2x80x94(CH2) 2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, or a single bond; a ring B and a ring C each are independently 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, 1,4-phenylene, or 1,4-phenylene in which at least one hydrogen is replaced by fluorine; and a ring D is 1,4-cyclohexylene, 1,4-phenylene or 1,4-phenylene in which at least one hydrogen is replaced by fluorine.
[10] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any one of the items [1] to [7] as the first component and at least one compound selected from the group of compounds represented by formulas (5) and (6) as a second component: 
wherein R2 and R3 each are independently alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and any hydrogen in the alkyl may be replaced by fluorine; X2 is xe2x80x94CN or xe2x80x94Cxe2x89xa1Cxe2x80x94CN; a ring E is 1,4-cyclohexylene, 1,4-phenylene, 1,3-dioxane-2,5-diyl, or pyrimidine-2,5-diyl; a ring F is 1,4-cyclohexylene, 1,4-phenylene, 1,4-phenylene in which hydrogen is replaced by fluorine, or pyrimidine-2,5-diyl; a ring G is 1,4-cyclohexylene or 1,4-phenylene; Z6 is xe2x80x94(CH2)2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, or a single bond; L3, L4 and L5 each are independently hydrogen or fluorine; and a, b and c each are independently 0 or 1.
[11] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any one of the items [1] to [7] as the first component and at least one compound selected from the group of compounds represented by formulas (7), (8) and (9) as a second component: 
wherein R4 and R5 each are independently alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and any hydrogen in the alkyl may be replaced by fluorine; a ring I and a ring J each are independently 1,4-cyclohexylene or 1,4-phenylene; L6, L7, L8 and L9 each are independently hydrogen or fluorine, and all of them are not hydrogen simultaneously; and Z7 and Z8 each are independently xe2x80x94(CH2)2xe2x80x94, xe2x80x94COOxe2x80x94 or a single bond.
[12] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any of the items [1] to [7] as the first component, at least one compound selected from the group of the compounds represented by formulas (2), (3) and (4) described in the above item [9] as the second component, and at least one compound selected from the group of compounds represented by formulas (10), (11) and (12) as a third component: 
wherein R6 and R7 each are independently alkyl having 1 to 10 carbon, in which any xe2x80x94CH2xe2x80x94 in the alkyl may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, but xe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94 are not adjacent, and any hydrogen in the alkyl may be replaced by fluorine; a ring K, a ring M and a ring N each are independently 1,4-cyclohexylene, pyrimidine-2,5-diyl, 1,4-phenylene, or 1,4-phenylene in which hydrogen is replaced by fluorine; and Z9 and Z10 each are independently xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or a single bond.
[13] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any one of the items [1] to [7] as the first component, at least one compound selected from the group of the compounds represented by formulas (5) and (6) described in the above item [10] as the second component, and at least one compound selected from the group of the compounds represented by formulas (10), (11) and (12) described in the above item [12] as the third component.
[14] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any one of the items [1] to [7] as the first component, at least one compound selected from the group of the compounds represented by formulas (7), (8) and (9) described in the above item [11] as the second component and at least one compound selected from the group of the compounds represented by formulas (10), (11) and (12) described in the above item [12] as the third component.
[15] The liquid crystal composition defined in the above item [8], comprising at least one silicon compound described in any of the items [1] to [7] as the first component, at least one compound selected from the group of the compounds represented by formulas (2), (3) and (4) described in the above item [9] as the second component, at least one compound selected from the group of the compounds represented by formulas (5) and (6) described in the above item [10] as the third component, and at least one compound selected from the group of the compounds represented by formulas (10), (11) and (12) described in the above item [12] as a fourth component.
[16] A liquid crystal composition comprising at least one liquid crystal composition defined in the items [8] and further comprising at least one optically active compound.
[17] A liquid crystal display using the liquid crystal composition defined in any of the items [8] to [15].
The compound (1) of the present invention is a compound having a SiH3 group at an end and 2 to 4 six-membered rings (hereinafter referred to as a bicyclic system to a tetracyclic system), and it is physically and chemically very stable under conditions on which a display is used. Further, six-membered rings, a bonding group and side chains constituting the compound (1) having a good mutual solubility, a low viscosity and a low threshold voltage are suitably selected, whereby the desired physical property values can optionally be controlled. The preferred compounds are shown below. 
Y1 and Y2 mean the same as those described in the item [1] described above.
Capable of being given as preferred Y1 is alkylene, alkyleneoxy, alkyleneoxyalkylene, alkenylene, alkenyleneoxy, alkenyleneoxyalkylene or alkyleneoxyalkenylene which has 1 to 10 carbon atoms. Among them, the most preferred group includes methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, methyleneoxy, ethyleneoxy, propyleneoxy, butyleneoxy, pentyleneoxy, hexyleneoxy, heptyleneoxy, methyleneoxymethylene, ethyleneoxymethylene, propyleneoxymethylene, methyleneoxyethylene, ethyleneoxyethylene, methyleneoxyproeylene, ethyleneoxypropylene, vinylene, 1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene, 3-butenylene, 2-prpenyleneoxy and 2-butenyleneoxy.
Capable of being given as preferred Y2 is alkyl alkoxy, alkoxyalkyl, alkenyl, alkenyloxy, alkenyloxyalkyl or alkyloxyalkenyl which has 1 to 10 carbon atoms, alkynyl, fluoroalkyl, fluoroalkyloxy, halogen, cyano and cyanoalkynyl. Among them, the particularly preferred groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, methoxypropyl, ethoxypropyl, propoxypropyl, vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 2-propenyloxy, 2-butenyloxy, 2-pentenyloxy, 4-pentenyloxy, 2-propenyloxymethyl, 2-propenyloxyethyl, 3-butenyloxymethyl, 3-methoxy-1-propenyl, 3-methoxy-1-pentenyl, 3-methoxy-2-pentenyl, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, xe2x80x94F, xe2x80x94Cl, xe2x80x94CN, xe2x80x94Cxe2x89xa1Cxe2x80x94CN, xe2x80x94CF3, xe2x80x94OCF3 and xe2x80x94OCF2H.
The compound in which one or both of Y1 and Y2 are optically active groups is particularly useful as a chiral dopant. Addition thereof to the composition makes it possible to prevent reverse twist domain from being produced.
The compound (1) can suitably be used as a component for a composition used for various displays including a TN type, an STN type, a TFT type and so on. Among the compounds (1), the bicyclic and tricyclic compounds show a low viscosity, and the tricyclic and tetracyclic compounds show a high isotropic phase transition temperature.
The compound (1) having two or more cyclohexane rings in a molecule shows a high isotropic phase transition temperature, a small xcex94n and a low viscosity. Further, the compound (1) having a dioxane ring or a pyrimidine ring shows a relatively large xcex94∈.
The compound (1) having at least one benzene ring in a molecule shows a relatively large xcex94n and a high liquid crystal orientational parameter and therefore is excellent. In particular, the compound (1) having two or more benzene rings in a molecule shows a particularly large xcex94n, a broad liquid crystal temperature range and a chemically high stability.
The compound (1) which is substituted with groups such as xe2x80x94F, xe2x80x94CN, xe2x80x94CF3, xe2x80x94OCF3 and xe2x80x94OCF2H so that the dipole moment grows larger in a molecular long axis direction has a large positive xcex94∈, a high isotropic phase transition temperature and a relatively low viscosity. The compound in which these groups are substituted on a benzene ring shows an excellent stability and a particularly large positive xcex94∈. Further, the compound in which plural groups are substituted on a benzene ring shows a larger xcex94∈.
The compound (1) which is substituted with xe2x80x94F so that the dipole moment grows larger in a molecular short axis direction has a large negative xcex94∈, a high isotropic phase transition temperature and a relatively low viscosity. The compound in which xe2x80x94F is substituted on a lateral side of a benzene ring shows an excellent chemical stability and a large negative xcex94∈. The compound having two or more xe2x80x94F shows a particularly large negative xcex94∈.
The compound (1) having double bonds on Z1, Z2 or Z3 shows a broad liquid crystal temperature range and a large elastic constant ratio, and therefore it is suitably used as a composition for STN. The compound (1) having a triple bond shows a large xcex94∈.
These matters make it possible to provide a novel liquid crystalline compound having desired physical properties by suitably selecting rings, side chains and/or bonding groups. Further, the compound (1) in which atoms constituting it are substituted with the isotopes shows the same characteristics and therefore can be used as well.
The composition of the present invention shall be explained below. This composition preferably contains 0.1 to 99.9% by weight of at least one compound (1) (hereinafter referred to as a first component) in order to allow excellent characteristics to be revealed. The amount is more preferably 1 to 80% by weight and further preferably 1 to 60% by weight.
The composition may comprise only the first component. It is allowed to be added as the second component, which is at least one compound (hereinafter referred to as a second A component) selected from the compounds (2), (3) and (4) described above or at least one compound (hereinafter referred to as a second B component) selected from the compounds (5) and (6) to the first component. At least one compound selected from the compounds (10), (11) and (12) can also be added as the third component for the purpose of controlling a threshold voltage, a liquid crystal phase temperature range, a birefringence, a dielectric anisotropy and a viscosity.
The compounds which are the respective components for the composition may be the analogues thereof comprising the isotopes of the respective elements since there is no large difference between the physical characteristics thereof.
In the second A component described above, the suitable examples of the compound (2) are (2-1) to (2-9); the suitable examples of the compound (3) are (3-1) to (3-97); and the suitable examples of the compound (4) are (4-1) to (4-33). 
In the formulas, R1 and X1 mean the same as those described in the item [9] described above.
These compounds (2), (3) and (4) have a positive dielectric anisotropy and are very excellent in heat stability and chemical stability, so that they are used primarily for a composition for TFT. When preparing a composition for TFT, an amount of the above compound falls in a range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight and more preferably 40 to 95% by weight based on the whole weight of a composition. The compounds (10) to (12) may further be added to the composition for the purpose of controlling a viscosity.
In the second B component described above, the suitable examples of the compounds (5) to (6) are (5-1) to (5-58) and (6-1) to (6-3) respectively. 
In the formulas, R2, R3 and X2 mean the same as those described in the item [10] described above.
These compounds (5) and (6) have a very large positive dielectric anisotropy, so that they are used mainly for the compositions for STN or TN. These compounds are used particularly for the purpose of reducing a threshold voltage. They are used as well for the purposes of controlling a viscosity and a birefringence and expanding a liquid crystal phase temperature range and also for the purpose of improving steepness. When preparing a composition for STN or TN, a use amount of the compounds (5) and (6) falls in a range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight and more preferably 40 to 95% by weight. A third component described later can further be added for the purpose of controlling a threshold voltage, a liquid crystal phase temperature range, a birefringence, a dielectric anisotropy and a viscosity.
When preparing a composition having a negative dielectric anisotropy which is suited for a vertical aligning mode (VA mode), preferably mixed is at least one compound (hereinafter referred to as a second C component) selected from the compounds (7) to (9). The suitable examples of the compounds (7) to (9) in the second C component are (7-1) to (7-3), (8-1) to (8-5) and (9-1) to (9-3) respectively. 
In the formulas, R4 and R5 mean the same as those described in the item [11] described above).
The compounds (7) to (9) have a negative dielectric anisotropy. The compound (7) having two six-membered rings is used mainly for the purpose of controlling a threshold voltage, a viscosity or a dielectric anisotropy. The compound (8) is used for the purpose of elevating the clearing point to expand a nematic range, reducing a threshold voltage and increasing a dielectric anisotropy.
The compounds (7) to (9) are used for a composition for a VA mode having a negative value of the dielectric anisotropy. If an amount thereof is increased, a composition is reduced in a threshold voltage but increased in a viscosity. Accordingly, as small amount as possible is preferred as long as a required value of the threshold voltage is satisfied. An amount of the compounds (7) to (9) is preferably 40% by weight or more, more preferably 50 to 90% by weight in the case of uses for a VA mode.
The compounds (7) to (9) are mixed in a certain case with a composition having a positive dielectric anisotropy for the purpose of controlling an elastic constant and a voltage transmission curve of the composition. An amount thereof is preferably 30% by weight or less.
In the third component described above, the suitable examples of the compounds (10) to (12) are (10-1) to (10-11), (11-1) to (11-12) and (12-1) to (12-6) respectively. 
In the formulas, R6 and R7 mean the same as those 5 described in the item [12] described above.
The compounds (10) to (12) have a small absolute value of a dielectric anisotropy and are close to neutrality. The compound (10) is used mainly for the purpose of controlling a viscosity or a dielectric anisotropy. Further, the compounds (11) and (12) are used for the purpose of elevating a clearing point to broaden a nematic range or controlling a dielectric anisotropy. If a use amount of the compounds (10) to (12) is increased, a composition is elevated in a threshold voltage and reduced in a viscosity. Accordingly, they are used preferably in a large amount as long as a required value of the threshold voltage is satisfied. An amount of the compounds (10) to (12) is 40% by weight or less, preferably 35% by weight or less in the case of uses for TFT. An amount in uses for STN or TN is 70% by weight or less, preferably 60% by weight or less.
A composition of the present invention contains 0.1 to 99% by weight of at least one of the compounds (1), whereby the excellent characteristics are revealed.
A composition is prepared by a publicly known method, for example, by dissolving various components by heating. Suitable additives are added if necessary, whereby the composition is optimized according to intended uses. Such additives are well known by a person averagely skilled in the art and described in detail in literatures. A chiral dopant induces a spiral structure of liquid crystal to provide distortion to thereby prevent inverse distortion. The following optically active compounds can be given as the examples of the chiral dopant. 
Usually, in the composition of the present invention, these optically active compounds are added to control a pitch in distortion. The pitch in distortion falls preferably in a range of 40 to 200 xcexcm in the case of the compositions for TFT and TN. In the case of the composition for STN, it falls preferably in a range of 6 to 20 xcexcm. Further, in the case of the composition for a bistable TN mode, it falls preferably in a range of 1.5 to 4 xcexcm. Two or more kinds of the optically active compounds may be added for the purpose of controlling a temperature dependency of the pitch.
The composition of the present invention can also be used as a liquid crystal composition for a G-H mode by adding dichroic dyes such as merocyanines, styryls, azo, azomethines, azoxy, quinophthalones, anthraquinones, tetrazines, or the like. The composition according to the present invention can also be used as a composition for NCAP prepared by micro-capsulizing nematic liquid crystal and Polymer Dispersed Liquid Crystal Display (PDLCD) prepared by forming a three-dimensional network polymer in the liquid crystal, for example, Polymer Network Liquid Crystal Display (PNLCD). It can also be used as a composition for Electrically Controlled Birefringence (ECB) mode and a DS mode
The compound (1) is produced by a conventional organic synthetic method. Suitably selected and combined are publicly known and conventional synthetic methods described in publications and magazines such as, for example, Organic Synthesis (John Wiley and Sons), Organic Reactions (John Wiley and Sons), Comprehensive Organic Synthesis (Pergamon Press) and Shin-Zikken Kagaku Koza (Maruzen).
Suitably selected and combined for introducing an Si part are publicly known and conventional synthetic methods described in publications and magazines such as, for example, Silicon in Organic Synthesis (Butterworths), Silicon Reagents for Organic Synthesis (Springer-Verlag) and Silicon Reagents in Organic Synthesis (Academic Press).
Routes shown below can be given as the specific examples. 
Y1, Y2, A1, A2, A3, A4, Z1, Z2, Z3, p and q each described above are the same as those described in the item [1] described above. Q1 is halogen, and Q2 is halogen or alkoxy. Mt is lithium, potassium, halogenated magnesium or halogenated zinc.
First, the compound (11) is reacted with metal such as magnesium and various organic metal reagents such as alkyllithium compounds, alkylzinc compounds, alkylpotassium compounds and alkylcadmium compounds, whereby an organic metal reagent (12) is prepared. This is reacted with tretrasubstituted silane such as tetraalkoxysilane and tetrahalosilane to obtain a silicon compound (13). The compound (13) is subjected to reducing treatment with a suitable reducing agent such as lithium aluminum hydride, diisobutylaluminum hydride, sodium borohydride, sodium cyanoborohydride and diborane-THF, whereby it is derived into a compound (1). When other substituents in the compound (13) are reduced with these reducing agents, suitable additives are used or the reaction conditions are controlled to selectively reduce only SiQ23.